Afarmer tosses a rope over a beam at the top of a barn. he ties one end of the rope to a bale of hay. he then raises the bale up to the barn loft by pulling down on the loose end of the rope.

why does the input force have to be greater than the force needed to lift the bale?

a. friction increase the effect of the input force.
b. friction eliminates the work input.
c. friction reduces the work input

Two red blood cells each have a mass of 9.0 multiply.gif 10-14 kg and carry a negative charge spread uniformly over their surfaces. the repulsion arising from the excess charge prevents the cells from clumping together. one cell carries −2.50 pc of charge and the other −3.10 pc, and each cell can be modeled as a sphere 7.5 μm in diameter. (a) what speed would they need when very far away from each other to get close enough to just touch? assume that there is no viscous drag from any of the surrounding liquid. answer is: 321 m/s how do i find this (b) what is the maximum acceleration of the cells in part (a)? answer is: 1.38e+10 m/s2 how did they find this answer

World class speed skaters can skate a 3,000-m course in about 4 minutes.what is their average speed for this course? a. 12.5 m/sb. 1.33 m/sc. 1.25 m/sd. 13.3 m/s

It is really hard for me right know